Eric Firing wrote:
> Michael Droettboom wrote:
>>
>> Eric Firing wrote:
>>> Mike,
>>>
>>> A bug was recently pointed out: axhline, axvline, axhspan, axvspan
>>> mess up the ax.dataLim. I committed a quick fix for axhline and
>>> axvline, but I don't think that what I did is a good solution, so
>>> before doing anything for axhspan and axvspan I want to arrive at a
>>> better strategy.
>>>
>>> What is needed is a clean way to specify that only the x or the y
>>> part of ax.dataLim be updated when a line or patch (or potentially
>>> anything else) is added. This is specifically for the case, as in
>>> *line, where one axis is in data coordinates and the other is in
>>> normalized coordinates--we don't want the latter to have any effect
>>> on the dataLim.
>>>
>>> This could be done in python in any of a variety of ways, but I
>>> suspect that to be most consistent with the way the transforms code
>>> is now written, relying on update_path_extends from _path.cpp, it
>>> might make sense to append two boolean arguments to that cpp
>>> function, "update_x" and "update_y", and use kwargs in
>>> Bbox.update_from_path and siblings to set these, with default values
>>> of True.
>> It seems we could do this without touching C at all. Just change
>> update_from_path so it only updates certain coordinates in the
>> bounding box based on the kwargs you propose. Sure, the C side will
>> be keeping track of y bounds even when it doesn't have to, but I
>> doubt that matters much compared to checking a flag in the inner
>> loop. It will compute the bezier curves for both x and y anyway
>> (without digging into Agg). It's hard to really estimate the
>> performance impact, so I'm necessarily pushing for either option, but
>> it may save having to update the C.
>
> Mike,
>
> I was somehow thinking that update_path_extents was changing things in
> place--completely wrong. So yes, it is trivial to make the change at
> the python level, and that is definitely the place to do it. I will
> try to take care of it this evening.
>
> In poking around, however, I came up with a couple of questions.
> Neither is a blocker for what I need to do, but each might deserve a
> comment in the code, if nothing else.
>
> 1) in _path.cpp:
>
> void get_path_extents(PathIterator& path, const agg::trans_affine& trans,
> double* x0, double* y0, double* x1, double* y1,
> double* xm, double* ym)
> {
> typedef agg::conv_transform<PathIterator> transformed_path_t;
> typedef agg::conv_curve<transformed_path_t> curve_t;
> double x, y;
> unsigned code;
>
> transformed_path_t tpath(path, trans);
> curve_t curved_path(tpath);
>
> curved_path.rewind(0);
>
> while ((code = curved_path.vertex(&x, &y)) != agg::path_cmd_stop)
> {
> if ((code & agg::path_cmd_end_poly) == agg::path_cmd_end_poly)
> continue;
> /* if (MPL_notisfinite64(x) || MPL_notisfinite64(y))
> continue;
> We should not need the above, because the path iterator
> should already be filtering out invalid values.
> */
> if (x < *x0) *x0 = x;
> if (y < *y0) *y0 = y;
> if (x > *x1) *x1 = x;
> if (y > *y1) *y1 = y;
> if (x > 0.0 && x < *xm) *xm = x;
> if (y > 0.0 && y < *ym) *ym = y;
> }
> }
>
>
> In the last 2 lines, why are xm and ym being clipped at 0, when x0 and
> y0 are not?
xm and ym are the minimum positive values, used for log scales.
Definitely worth a comment.
>
> 2) It looks like update_path_extents throws away orientation by always
> returning x0 and y0 as the minima. Bbox.update_from_path is therefore
> doing the same. This doesn't hurt in present usage, since orientation
> is not needed for dataLim, but it seems a bit surprising, and worth a
> comment at least. Am I again missing something obvious?
>
I think I'm missing something. (Choices in my code are always obvious
to *me*, and any mistakes are invisible... ;) Are you suggesting that
if a line has x decreasing then x0 > x1? What if it boomerangs? I
think it's simplest to keep data limits in a consistent order. View
limits are another issue, of course.
Mike
--
Michael Droettboom
Science Software Branch
Operations and Engineering Division
Space Telescope Science Institute
Operated by AURA for NASA
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